DIFFERENTIAL-EFFECTS OF LIDOCAINE ON DEFIBRILLATION THRESHOLD WITH MONOPHASIC VERSUS BIPHASIC SHOCK WAVE-FORMS

Background Defibrillation waveforms and antiarrhythmic drugs have disp arate effects on myocardial excitability and refractoriness, making it likely that antiarrhythmic drugs will interact with one waveform diff erently than with another. The aim of the present study was to determi ne if the increase in defibrillation threshold (DFT) induced by lidoca ine is similar for electrical shocks with monophasic and biphasic wave forms. Methods and Results Twenty-six pentobarbital-anesthetized farm- raised pigs were instrumented with pacing catheters and epicardial def ibrillation electrodes. Each pig was assigned to one of four groups: ( 1) monophasic shock waveform and placebo (5% dextrose in water [D5W]) (n=7), (2) monophasic shock waveform and lidocaine (n=7), (3) biphasic shock waveform add placebo (D5W) (n=5), or (4) biphasic shock wavefor m and lidocaine (n=7). DFT was measured at baseline and subsequently d uring treatment (D5W or lidocaine). In the monophasic waveform groups, DFT increased from baseline in response to lidocaine by 92% (P<.0001) , whereas DFT values in response to D5W did not change. In the biphasi c waveform groups, DFT values did not change from baseline in response to lidocaine (P=NS), whereas DFT values from baseline in response to D5W significantly decreased by 29% (P=.04). In the monophasic waveform groups, the change in DFT from baseline in response to lidocaine was significantly different than the change from baseline in response to D 5W (92+/-29% versus -0.5+/-29%, respectively) (P<.0002). In the biphas ic waveform groups, however, the change in DFT from baseline in respon se to lidocaine was similar to the change from baseline in response to D5W (-5.66+/-15% versus -29+/-17%, respectively) (P=.48). Furthermore , the change in DFT from baseline in response to lidocaine differed si gnificantly between monophasic and biphasic waveform groups (92+/-29% versus -5.66+/-15%) (P<.0002), whereas the change from baseline in res ponse to D5W did not differ between monophasic and biphasic waveforms (-0.5+/-29% versus -29+/-17%) (P=.34). Conclusions Compared with place bo groups, DFT values increased during lidocaine treatment to a much g reater degree in the monophasic waveform group than in the biphasic wa veform group receiving lidocaine. These data support our hypothesis th at antiarrhythmic drugs can affect the defibrillation efficacy of mono phasic waveforms differently than that of biphasic waveforms.